Currently, lithographic printing is the process in most common use for producing newspapers and magazines. Lithographic printing involves the preparation of plates bearing the image to be printed, which plates are mounted on a plate cylinder. An ink image produced on the plate cylinder is transferred to an offset cylinder that carries a rubber blanket. From the blanket, the image is applied onto paper or any other printing medium, termed the substrate, which is fed between the offset cylinder and an impression cylinder. For a wide variety of well-known reasons, offset litho printing is suitable, and economically viable, only for long print runs.
More recently, digital printing techniques have been developed that allow a printing device to receive instructions directly from a computer without the need to prepare printing plates. Amongst these are color laser printers that use the xerographic process. Color laser printing systems using dry toners are suitable for certain applications, but they do not produce images of a photographic quality acceptable for publications such as magazines.
A process that is better suited for short run high quality digital printing is used in the HP-Indigo digital printing press. In this process, an electrostatic image is produced on an electrically charged image bearing cylinder by exposure to laser light. The electrostatic charge attracts oil-based inks to form a color ink image on the image bearing cylinder. The ink image is then transferred by way of a blanket cylinder onto the substrate.
Inkjet and bubble jet processes are commonly used in home and office printing systems. In these processes droplets of ink are sprayed onto a final substrate in an image pattern. In general, the resolution of such processes is limited due to wicking by the inks into paper substrates, unless coated paper is used.
Various printing devices have also previously been proposed that use an indirect inkjet printing process, this being a process in which an inkjet print head is used to print an image onto the surface of an intermediate transfer member, which is then used to transfer the image onto a substrate. The intermediate transfer member may be a rigid drum or a flexible belt (e.g. guided over rollers, or mounted onto a rigid drum), also herein termed a blanket.